1. Field of the Invention
The invention lies in the field of the preparation and application of aqueous polymer dispersions. The dispersions are prepared through emulsion polymerization of olefinic unsaturated monomers in the presence of radical initiators. They are further processed with the addition of suitable additives and auxiliary agents, for example, into emulsion paints, dispersion adhesives, spread coating compounds to coat paper, coating compounds to coat the back of carpets, and compounds to manufacture latex foam.
2. Description of the Prior Art
Polymer dispersions must be stable not only during preparation but also during further processing. In particular, they must be adequately stable with respect to shear forces, electrolytes and frost-thaw cycles. They must be compatible with additives, for example, with pigments and fillers. When coating substrates, they must be capable of interacting with them so that the polymer adheres well to the substrate.
With respect to these requirements, the kind and quantity of the auxiliary agents and the composition and structure of the polymer at the surface of the polymer particles are of importance. There are various methods for modifying the surface of polymer particles. One method consists of introducing hydroxyl groups. This method makes it possible to set the interfacial hydrophilia. The introduction of polyol groups has proven to be especially effective. This can be done by known methods, during or after emulsion polymerization.
In Ullmann's Encyklopadie der technischen Chemie, 4th edition, Vol. 19, page 370, right column, 1.3.4 emulsion polymerization, the preparation of poly(vinyl acetate)-dispersions through emulsion polymerization of vinyl acetate in the presence of a radical initiator and poly(vinyl alcohol) as protective colloid is described. During polymerization a part of the poly(vinyl acetate) is grafted onto the poly(vinyl alcohol). Thus, the product is not uniform. Evidently, it contains a graft product in addition to poly(vinyl alcohol) and/or poly(vinyl acetate). The latter cannot be separated or can only be separated with great expense from the graft product. Nonuniformity of polymer dispersions is a drawback for some applications.
In European Published Patent Application No. 0 054 685, the preparation of aqueous polymer dispersions with polymer particles exhibiting glycol groups is described. In a first process step an aqueous polymer dispersion is obtained through emulsion polymerization of a mixture comprising 85 wt. % of vinyl acetate and 15 wt. % of glycidyl methacrylate in the presence of a radical initiator. In a second process step the polymer dispersion is treated with a sodium hydroxide solution. In so doing, the epoxide groups originating from the first process step are hydrolyzed forming glycol groups (Example 3 ). The polymer dispersions obtained contain, in the aqueous phase, substantially no dissolved macromolecular substances. The glycol groups contribute negligibly to the stability of the dispersions.